Pseudorandom Noise (PRN) codes are often employed as ranging codes in systems where it is desirable to determine the range or distance a PRN receiver is from a PRN transmitter. Typically, the range or distance between the PRN transmitter and PRN receiver is determined based on the data carried by the PRN codes. While PRN codes themselves do not have information for range determination, PRN codes are the means for the PRN receiver to determine the ranging accuracy. Typically, systems that employ PRN codes as ranging codes do so by finding the ranging codes of a PRN transmitter by receiving the ranging code with a PRN receiver and correlating the ranging code with a local replica within the PRN receiver. Such systems include, for example, Code Division Multiple Access (CDMA) based navigation systems such as, for example, global positioning systems (GPS), other Global Navigation Satellite Systems (GNSS), positioning systems (such as the Russian GLONASS system), or pseudolites (for example, a terrestrial positioning system using fixed ranging code transmission towers, or aerial positioning systems using balloons or manned or unmanned aircraft). In other aspects, such systems also include, for example, CDMA-based communications systems or Time Division Multiple Access (TDMA) based communication systems configured to use PRN ranging signals.
Conventional systems using PRN codes for ranging purposes generally are based on the PRN receiver's ability to correlate a received PRN code from the PRN transmitter with a local replica (stored or generated by the PRN receiver). When a PRN code is transmitted by the PRN transmitter and received by the PRN receiver and correlated by the PRN receiver with a local replica, the PRN receiver is able to determine an estimate of range between the PRN receiver and the PRN transmitter (determined by correlating the PRN code with the local replica) as well as any Doppler effects on the received PRN code. The characteristics of correlation between a received PRN code and a local replica are greatly influenced by the chip rate of the PRN code which is sent. Typically, a higher chip rate (e.g. a rate at which the PRN code chips transition) of a PRN code will provide for greater ranging accuracy and better time of arrival error estimation because there is a sharper autocorrelation peak that is generated when correlating the received PRN code with a local replica. However, in conventional systems, there are also significant drawbacks to employing a PRN code with a higher chip rate. First, PRN codes with higher chip rates require greater signal bandwidth. Further, conventional PRN receiver hardware typically includes a filter or pre-filter intended to attenuate noise and/or interfering signals outside that bandwidth. However, this filtering will inherently filter part of the received PRN code's bandwidth and unintentionally reduce signal resolution. This has the intrinsic effect of filtering out the high frequency components of PRN codes of high chip rates. This filtering performed by PRN receivers render higher chip rate PRN codes ineffective since the higher frequency components of the PRN code with higher chip rates are typically filtered out.